1. Field of the Invention
This invention relates to an engraver, and more particularly, systems and methods for automatically changing tools or components mounted on an engraving head, switching engraving heads and verifying a tool situated on the engraving head on the engraver.
2. Description of the Related Art
The basic principle of electro-mechanical engraving of a gravure cylinder involves rotating a plated cylinder while actuating an electronically driven tool or stylus which cuts or engraves engraved areas, cells or lines of engraved areas into a surface of the plated cylinder. The engraved cylinder is normally used in a web-type gravure printing press for printing paper, plastic, metallic film material or other printed material. In the gravure printing process, the engraved cylinder is flooded with ink, and a doctor blade wipes off excess ink from the surface of the cylinder so that the engraved cells or lines of cells contain an appropriate amount of ink which is transferred to the material being printed.
To obtain a high quality print, it is necessary that the cells be very accurately placed, located or engraved on the cylinder surface, usually within one or two microns of a desired predetermined location. The depth of the engraved cells must also be accurately controlled since the depth determines the amount of ink transferred which, in turn, determines the shade of gray in a black/white print, for example. In a color print, the amount of ink transferred to the paper or materials is even more critical since multiple colors are typically mixed to produce various shades of all possible colors. A slight variation in the desired amount of ink affects not only the color, but, more importantly, the density of the desired color.
In order to properly control the depth of the cells, the relative location between the plated cylinder and the electrically driven tool, which is typically a diamond stylus, must be accurately controlled. In order to ensure that the stylus is maintained at a constant distance from the plated cylinder as the cylinder rotates in the engraving process, the engraving head containing the stylus is provided with a diamond shoe tool which contacts the cylinder to maintain a desired predetermined spacing between the stylus and the cylinder.
When the stylus exits an engraved area or cell, a burr of material is commonly created around the edges of the cell, and the burr material, is removed by a diamond burr cutter mounted on the engraving head adjacent to location of the diamond stylus and the diamond shoe tool. Past burr cutters have comprised diamond tools having a cutting edge which is located over the center of an engraved cell or row of engraved cells to remove the burr material. The alignment between the burr cutter and the cylinder would vary with variations in the diameter of the cylinder such that it was necessary for an operator to perform an alignment operation and to place the cutter in tangential engagement with the cylinder surface whenever the cylinder diameter was changed.
U.S. Pat. No. 5,475,914 illustrates a simplified system and method showing tools on the engraving head formed with a cartridge-style construction. For example, a cartridge diamond stylus is provided having a trapezoidal cross section for facilitating positive registration and position of the stylus within the engraving head. Other tools, such as a shoe and/or burr cutter are provided in a detachable cartridge arrangement to facilitate quick mounting and replacement of an existing shoe or burr cutter, respectively, such that the shoe or burr cutter also became aligned and registered on the engraving head.
It was not uncommon that, during the engraving process, one or more of the tools on the engraving head became worn, broken or otherwise need to be replaced for various reasons. For example, it was not uncommon that, when changing from one engraving job to another engraving job, it was sometimes necessary to change engraving stylus. In this regard, multiple styli were typically available with included cutting angles of between 90 and 145 degrees in five degree increments. One engraving job may require the use of a stylus having a 100 degree stylus angle, while a second engraving job may require the use of a stylus having a 135 degree cutting angle. Moreover, a single engraving job may require the use of several styli having different cutting angles.
It was not uncommon that other tools mounted on the engraving head had to be changed periodically as well. Sometimes, the tools were manually changed at periodic maintenance intervals after a tool had a predetermined number of engraving hours thereon. If a stylus would happen to break between such maintenance intervals and such break was not detected, then the engraver would continue attempting to perform engraving with the broken stylus. This sometimes resulted in an inferior or unacceptable engraving quality. If this occurred, then the broken stylus caused the surface of the cylinder to be damaged, sometimes beyond repair to a degree that the entire cylinder became scrap.
Unfortunately, the changing of tools on the engraving head was a time consuming manual process. The engraving head had to be halted or stopped during the changeover, thereby resulting in engraving downtime.
Also, there was no convenient method or system for using multiple tools, such as multiple styli, without changing the tools.
Still another problem is that it would sometimes occur that due to operator error, for example, the stylus mounted on the engraving head was incorrect because, for example, it had an incorrect cutting angle. Some engraving systems of the past could optically detect a broken stylus, but they could not verify its cutting angle.
Accordingly, there is a need for an improved engraving system and method which facilitates a quick and automatic change over of one or more tools on one or more engraving head, which can provide multiple tool set capability and which has tool verification capability.